Presses for the manufacture of dimensionally stable pressed blanks from powdered material generally have a die, at least one upper ram and at least one lower ram which compact the powdered material in the cavity of the die from opposed sides. For example, the upper and lower rams are coupled to the slide and piston rod of a hydraulic cylinder that are mounted on the press frame. The powdered material is fed to the die bore by means of a suitable filling device where the position of the lower ram normally predetermines the filling height or filling volume. After the material is compressed the compact is removed from the die bore.
Presses of this type use different designs. So-called single-sided presses have stationary lower rams and dies. Double-sided presses move the die either floatingly or forcibly with the lower ram being fixed in place or movable. The so-called expulsion method or the withdrawal method is employed to demould the compact. The expulsion method involves moving the compact out of the stopped die by means of the lower ram whereas the lower ram is stationary and the die is moved in the withdrawal method.
Normally, the compression tools are not mounted directly on the adjustable drives, but are via adaptors. Thus, for instance, the die is clamped on a die retainer plate which, if movable, is coupled in turn to an adjustable drive by means of force-transmitting elements. The same applies to the upper and lower rams which are mounted on appropriate retainer plates. This allows to incorporate different compression tools in an existing press.
In the state of the art, a press of the type described is designed according to which demoulding principle is adopted. A conversion to the respective other demoulding principle normally is out of consideration.
The control or regulation of a compression procedure requires that at least two parameters should be known. On one hand, the compression force is measured to determine the maximum force by which the powder is compressed. In case of need, however, the run of the compression force of tools over the path or over time during the compression procedure is helpful as well. A further parameter is the position of the upper and lower rams with regard to a reference which usually is constituted by the upper edge of the die. It is known that influences by temperature and the compression forces result in length variations to the press frame, force-transmitting elements, and tools. Although the position of tools may be measured via their adaptors by means of suitable measuring systems the determinations of positions are not sufficiently precise unless a correction is made thereto via the respective temperature and compression force. Apart from this, there is a risk of the measuring systems themselves or their holder experiencing temperature-dependent end even compression force-dependent deformations and, therefore, induce inaccuracies in measurements.
From DE 102 54 656 B4, the entire contents of which is incorporated herein by reference, a typical hydraulic press has become known in which a die retainer plate and a plurality of ram carriers (adaptors) are variably mounted in the press frame via hydraulic drives. The known press provides for supporting devices which support the ram carriers at a press end position relative to the basic body of the press frame. DE 3142126 B1, the entire contents of which is incorporated herein by reference, has made known a press for the manufacture of stepped, dimensionally stable powder-based compacts from a ceramic material in which seating plates which carry lower rams are all movable hydraulically from a base plate and, in the press end position, rest as seating plates on adjustable mechanical stops of the base plate. The seating plates can be moved upwardly together by steps for the expulsion of the compacts after the withdrawal of the die and release of the compact's circumferential surface contacting the die up to the respective release of the next contact surface. In the press end positions defined by fixed stops, the counterforce or supporting force is generated by mechanical stops in either press.
From DE 103 00 722 B3, the entire contents of which is incorporated herein by reference, a press has become known in which an upper carriage and a lower carriage are guided vertically for the mounting an upper slide and a lower slide. The guide column is attached to a frame table on which also the die retainer plate is mounted. A no-wear guidance of the retainer plates is performed by the fact that the carriages are joined to the hydraulic drive via an angle balancing element and a lateral compensation element.
It is the object of the invention to provide a press for the manufacture of dimensionally stable compacts from powdered material that can easily be adapted to the desired removal/demoulding of the compact from the die bore and which further allows for a low-error determination of the positions of tools.